Mahouka Koukou no Rettousei - Shiba Tatsuya Ansatsu Keikaku is a Manga/Manhwa/Manhua in english language, Action series, english chapters have been translated and you can read them here. You are reading chapters on www.mgeko.nl fastest updating comic site. The Summary is

The Spring of 2094 AD. A young girl whose calling is assassination, Hashibami Yuki, is witnessed by a young middle school boy at the scene of a crime.
Supressing misgivings about erasing a young middle-schoolboy, Yuki’s superior abilities cannot compete at all. The name of the mysterious boy is Shiba Tatsuya.
If the opponent was a normal boy,
If the opponent was not a magician,
If the opponent was not Shiba Tatsuya—
An "irregular" boy and an "assassin" girl. The meeting of these two will alter fate and bring misfortune.